Metabolism of the arylamide herbicide propanil. I. Microsomal metabolism and in vitro methemoglobinemia

David C. McMillan, James P. Freeman, Jack A. Hinson

Research output: Contribution to journalArticlepeer-review

45 Scopus citations


Methemoglobinemia produced by exposure to the herbicide propanil (3,4-dichloropropionanilide) is thought to be mediated by toxic metabolites formed during the hepatic clearance of the parent compound. We examined the metabolism of propanil and 3,4-dichloroaniline in rat liver microsomes to identify metabolites that may be involved in propanil-induced methemoglobinemia. The major pathway of propanil metabolism in microsomal incubations was acylamidase-catalyzed hydrolysis to 3,4-dichloroaniline. The reaction did not require NADPH, and was inhibited by the acylamidase inhibitors paraoxon and sodium fluoride. Oxidized metabolites were isolated by high-performance liquid chromatography, and identified as 2′-hydroxypropanil and 6-hydroxypropanil by comparison of their mass and nuclear magnetic resonance spectra to those of synthetic standards. Major microsomal metabolites of 3,4-dichloroaniline were 6-hydroxy-3,4-dichloroaniline and N-hydroxy-3,4-dichloroaniline. Both N-hydroxy-3,4-dichloroaniline and 6-hydroxy-3,4-dichloroaniline directly oxidized hemoglobin in rat erythrocyte suspensions in a concentration-dependent manner; however, the potency of N-hydroxy-3,4-dichloroaniline was at least an order of magnitude greater than that of 6-hydroxy-3,4-dichloroaniline.

Original languageEnglish (US)
Pages (from-to)90-101
Number of pages12
JournalToxicology and Applied Pharmacology
Issue number1
StatePublished - Mar 15 1990
Externally publishedYes

ASJC Scopus subject areas

  • Toxicology
  • Pharmacology


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